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Evolution and the Theory of Natural Selection What is Evolution? The change in gene frequencies in a population over time.

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Presentation on theme: "Evolution and the Theory of Natural Selection What is Evolution? The change in gene frequencies in a population over time."— Presentation transcript:


2 Evolution and the Theory of Natural Selection

3 What is Evolution? The change in gene frequencies in a population over time

4 Charles Darwin (1809-1882) Born in England Attended medical school, HATED IT, and dropped out to become a priest Liked to stuff birds instead of dissect humans Didn’t like grave robbing for bodies Boarded the H.M.S. Beagle for a 5 year UNPAID journey as a naturalist


6 Journey of the H.M.S. Beagle

7 Alfred Russel Wallace (1823-1913) Presented a paper with identical ideas as Darwin on July 1, 1858 at the Linnaean Society meeting Was a botanist who came up with virtually the same concept of natural selection more or less independently through his studies on the Malay archipelago. Darwin panicked because he was not ready with his book yet!

8 Where did Darwin and Wallace get the idea of evolution?

9 Jean Baptiste Lamarck (1744-1829) Lamarck claimed that evolution was driven by "use vs. disuse" A used structure will become larger, stronger and more important. A disused structure will atrophy and become VESTIGIAL.

10 Theory of “Use vs. Disuse” The long necks of giraffes were due to their stretching for food, and giraffes passed their stretched necks on to their offspring. Similarly, the big, “ripped” muscles developed by the village blacksmith with all his hammering and slinging of heavy metal objects would be expected to be passed on to his offspring.

11 Theory of “Acquired Characteristics” Lamarck claimed that traits acquired during an organism's lifetime could be inherited by that organism's offspring.

12 Georges Cuvier (1769-1832) Created Paleontology (The study of fossils) He noted that deeper layers of sedimentary rock had diversity of organisms far different from present day life found in more recent layers Proposed the idea of extinction based on fossils

13 James Hutton (1726-1797) A Scottish geologist who challenged Cuvier's view in 1795 with his idea of GRADUALISM Proposed that large changes in the earth's surface could be caused by slow, constant processes such as erosion.

14 Charles Lyell (1797-1875) Earth processes had been going on constantly, and could explain the appearance of the earth. This theory, uniformitarianism, was a strong basis for Darwin's later theory of natural selection.

15 Thomas Malthus (1766-1834) Suggested that much of humanity's suffering (disease, famine, homelessness and war) was the inevitable result of overpopulation: humans reproduced more quickly than their food supply could support them. Malthus showed that populations, if allowed to grow unchecked, increase at a geometric rate.

16 Darwin made some profound observations, from which he inferred some brilliant conclusions... Observation #1. All species have huge potential fertility Observation #2. Except for seasonal fluctuations, populations tend to maintain a stable size. Observation #3. Environmental resources are limited.

17 Inference #1 The production of more individuals than the environment can support leads to a "struggle for existence," with only a fraction of offspring surviving in each generation.

18 Observations Observation #4: No two individuals in a population are exactly alike Observation #5: Much of the observed variation in a population is heritable

19 Inference #2 Survival in this "struggle for existence is not random, but depends, in part, on the hereditary makeup of the survivors. Those individuals who inherit characteristics that allow them to best exploit their environment are likely to leave more offspring than individuals who are less well suited to their environment.

20 Inference #3 Unequal reproduction between suited and unsuited organisms will eventually cause a gradual change in a population, with characteristics favorable to that particular environment accumulating over the generations.

21 SO WHAT IS THIS THEORY OF NATURAL SELECTION? It can be broken down into four basic tenets, or ideas

22 Theory of Natural Selection 1. Organisms are capable of producing huge numbers of offspring. 2. Those offspring are variable in appearance and function, and some of those variations are heritable.

23 Theory of Natural Selection 3. Environmental resources are limited, and those varied offspring must compete for their share. 4. Survival and reproduction of the varied offspring is not random. Those individuals whose inherited characteristics make them better able to compete for resources will live longer and leave more offspring than those not as able to compete for those limited resources.


25 Evolution 1.Theory - an accepted hypothesis that has been tested over and over again without yet being disproved 2.Definition - Evolution is the change in the overall genetic makeup of a population over time 3.Three Basic Components a. Individuals cannot evolve. Populations evolve. b. Natural selection is the mechanism of evolution. c. Evolution occurs by chance.

26 Evolution Evolution is the genetic change in a population over time Populations are a group of interbreeding individuals belonging to the same species and sharing a common geographic area Natural selection favors individuals, so multiple generations must be examined

27 What is speciation and who studies it? Speciation is the creation of a new species Scientists who study the processes and mechanisms that lead to such speciation events are called EVOLUTIONARY BIOLOGISTS.


29 Allopatric Speciation A population becomes physically separated from the rest of the species by a geographical barrier that prevents interbreeding. Because gene flow is disrupted by this physical barrier, new species will form.

30 Sympatric Speciation Two populations are geographically close to each other, but they are reproductively isolated from each other by different habitats, mating seasons, etc.


32 Reproductive Barriers A reproductive barrier is any factor that prevents two species from producing fertile hybrids, thus contributing to reproductive isolation. Habitat Isolation Temporal Isolation Behavioral Isolation Mechanical Isolation Gametic Isolation



35 Species A SPECIES is a group of similar organisms that can mate to produce fertile, viable offspring. Different species are, by definition, REPRODUCTIVELY ISOLATED from one another.


37 Adaptive Radiation Adaptive Radiation - Evolutionary process in which the original species gives rise to many new species, each of which is adapted to a new habitat and a new way of life. E.g. Darwin's Finches




41 Adaptive Radiation of Hominids

42 Evidence for Evolution HOMOLOGY is a characteristic shared by two species (or other taxa) that is similar because of common ancestry. Artificial Selection Farmers had been conducting this controlled breeding of livestock and crops for years in order to obtain the most milk from cows or the best cobs from corn plants.

43 Evidence for Evolution Paleontology - Study of Fossils a. Fossil - preserved evidence of past life b. Radioactive Dating - method by which fossil age can be determined by the amount of organic matter remaining in the specimen. This is possible because some substances break down at a known rate (half-life).


45 Types of homology morphological homology – species placed in the same taxonomic category show anatomical similarities. ontogenetic homology - species placed in the same taxonomic category show developmental (embryological) similarities. molecular homology - species placed in the same taxonomic category show similarities in DNA and RNA.

46 MORPHOLOGICAL HOMOLOGY Structures derived from a common ancestral structure are called: HOMOLOGOUS STRUCTURES




50 Ontogenetic Homology The human embryo has gills, a tail, webbing between the toes & fingers, & spends its entire time floating and developing in amniotic fluid has similar salt concentration as ocean water


52 MORPHOLOGICAL HOMOLOGY A structure that serves the same function in two taxa, but is NOT derived from a common ancestral structure is said to be an ANALOGOUS STRUCTURE


54 Examples of Analogous structures: wings of bat, bird, and butterfly walking limbs of insects and vertebrates cranium of vertebrates and exoskeleton head of insects

55 Molecular Homology



58 Types of Evolution Divergent Evolution - Method of evolution accounting for the presence of homologous structures. Multiple species of organisms descended from the same common ancestor at some point in the past. Convergent Evolution - Method of evolution accounting for the presence of analogous structures. Organisms of different species often live in similar environments, thus explaining the presence of features with similar functions.


60 An ongoing process Evolution can be considered a process of "remodeling" a population over the course of many generations, with the driving force being the natural selection factors that favor one form over another in specific environments.

61 Vestigial Structures Have marginal, if any use to the organisms in which they occur. EXAMPLES: femurs in pythonid snakes and pelvis in cetaceans (whales) appendix in humans coccyx in great apes




65 Rate of Evolution Gradual evolution occurs where the increment of change is small compared to that of time. Punctuated evolution occurs where the increment of change is very large compared to that of time in discrete intervals, while most of the time there is virtually no change at all.




69 Natural Selection in Action Industrial melanism

70 Natural Selection in Action Camouflage

71 Natural Selection in Action Mimicry Coral vs. King Snakes: Red on yellow, kill a fellow, red on black won’t hurt Jack

72 Natural Selection in Action Mimicry Monarch or Viceroy Butterfly

73 Natural Selection in Action Warning Coloration

74 Natural Selection in Action Disruptive Coloration

75 Natural Selection in Action Counter Shading

76 Natural Selection in Action Eye spots

77 Causes of Evolution 1.Mutations - random changes in genetic material at the level of the DNA nucleotides or entire chromosomes 2.Natural Selection - most important cause of evolution; measured in terms of an organism's fitness, which is its ability to produce surviving offspring a. Stabilizing Selection - average phenotypes have a selective advantage over the extreme phenotypes b. Directional Selection - phenotype at one extreme has a selective advantage over those at the other extreme c. Disruptive Selection - both extreme phenotypes are favored over the intermediate phenotypes

78 Natural selection favors the average individuals within a population

79 Natural selection favors on one of the extreme variations within a species

80 Individuals with both extreme phenotypes are selected for


82 Causes of Evolution 3. Mating Preferences - Organisms usually do not choose their mates at random, thus the selection process can cause evolution 4. Gene Flow - Transfer of genes between different populations of organisms. This situation leads to increased similarity between the two populations 5. Genetic Drift (Founder Effect & Bottleneck) - Situation that results in changes to a population's gene pool caused by random events, not natural selection. This situation can have drastic effects on small populations of individuals. Common on islands.

83 Gene Flow

84 Genetic Drift



87 Founder Effect

88 Bottleneck Effect



91 Hardy-Weinberg HW law states --> original of a genotypes alleles remains CONSTANT HW Equilibrium... is defined algebraically any gene with 2 allelic forms... A and a let frequency of one allele (A) = p & frequency of other allele (a) = q then by definition, p + q = 1 HW equation... (p + q)2 = p2 + 2 pq + q2 = 1 AA Aa aa



94 Hardy-Weinberg What are the H-W frequencies for the following population of plants with different colored flowers? 63 red (RR), 294 pink (Rr) and 343 white (rr) = 700 plants, 1400 genes or alleles Is the population in H-W equilibrium?


96 H-W Equilibrium Is the population below in HW Equlibrium? 50 individuals (AA), 50 individuals (Aa), 50 individuals (aa), 300 alleles






102 Anthropological Evolution The history of hominids (Present day & extinct)

103 Phylogeny The history of hominid life depicted as a branching tree Earliest hominids are placed at the trunk Each branch represents a new species which inherits many traits from the ancestor but also has a new trait which appear for the 1 st time


105 Phylogenetic Tree

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